I used to think that, and indeed a computer can run any equations you want. However with analogue you're getting a bunch of interesting-sounding equations without having to think of them and write them down, and that's the "analogue sound." Analogue circuitry isn't a perfect math processor the way digital is, only an approximation, and the deviations from perfection are useful.

Especially if you get into synths. A digital sine wave oscillator is doing sin(time*frequency)*gain. An analogue one is designed to produce a close to perfect sine wave at a certain set point, but you make it able to be varied around that set point by replacing some of the components with adjustable ones in somewhat ad-hoc ways, and see what it sounds like. The frequency may be set by a 3-stage RC circuit, you replace all the Rs with vactrols and see what happens, now the impedance changes as well as the frequency and it might affect other parts of the circuit. You may one-point calibrate it to 1 volt per octave but it won't be linear.